Construction for cryogenic cables

ABSTRACT

Superconductive strings are stranded with insulating strings to form a rope which is inserted in a pipe otherwise filled with or passed through by coolant to obtain cryogenic conditions.

United States Patent Inventor August Beck Langenhagen, Germany App]. No. 880,995 Filed Nov. 28, 1969 Patented Sept. 14, 1971 Assignee Kabel-und Metallwerke Gutehoffnungshutte Aktiengesellschaft Hannover, Germany Priority Dec. 4, 1968 Germany P 18 12 613.1

CONSTRUCTION FOR CRYOGENIC CABLES 14 Claims, 7 Drawing Figs.

US. Cl 174/15, 174/27,174/29,I74/D1G.6

Int. Cl 1101b 7/34 Field of Search 174/15, 15

C, 28, 29, 128, 27, DIG. 7; 335/216; 333/99 S [56] References Cited UNlTED STATES PATENTS 2,879,317 3/1959 Wreford 174/15 3,106,600 10/1963 Crosby 174/15 3,187,235 6/1965 Berlincourt et al. 174/15 X 3,293,009 12/ l 966 Allen at al. 174/D1G. 7

3,444,307 5/1969 Kafka 174/27 X 3,448,222 6/1969 Greber 174/27 X Primary Examiner-Lewis H. Myers Assistant Examiner-A. T. Grimley Attorney-Smyth, Roston & Pavitt ABSTRACT: Superconductive strings are stranded with insulating strings to form a rope which is inserted in a pipe otherwise filled with or passed through by coolant to obtain cryogenic conditions.

CONSTRUCTION FOR CRYOGENIC CABLES The present invention relates to an arrangement for supporting one or several superconductors in the interior of a cryogenic cable. Low-temperature cables, also called cryogenic cables, have been used for the transmission of electrical energy. The conductors in such a cable are disposed in the interior of a pipe or tube filled, for example, with liquid helium. Protection against inflow of heat from the environment if provided by means of one or more additional pipes concentrically receiving the pipe which contains the conductors and is filled with liquid helium. For example, four concentrical pipes can be provided and arranged as follows: The space between the innermost pipe (containing the conductors) and the second one with next larger diameter is evacuated and a high vacuum is maintained during operation. The space between the second pipe and the third pipe receiving the second one is, for example, filled with liquid nitrogen in order to provide a controlled distribution of the temperature gradient from the innermost tube toward the outer environment. The space between the third and the last pipe receiving the third pipe is again evacuated, and the last outermost pipe is presumed to assume ambient temperature.

The conductors themselves for such a cable are known to include two concentrically disposed carriers, the inner carrier thereof has onits outer surface a layer of particularly superconductive material while the inner surface of the outer carrier is likewise provided with a layer of such a material. It is furthermore known, to use plural conductors in a divided, multiconductor system instead of a single conductor with comparatively large cross section; the conductors of the plurality have relative smaller cross section and are connected in parallel.

Lead, niobium and some niobium alloys and compounds have become known as being suitable superconductive material. Accordingly, the conductors themselves can be made of such a superconductive material. However, transmission of electrical energy is usually restricted to a thin layer near the surface of a conductor because of current displacement (skin effect). Therefore it suffices if a carrier is in fact provided with a thin layer of such a superconductive material. The carrier will be of a different material, usually a less expensive one, and can be made of metal or plastic. Such a layer is provided onto the carrier by means of electrolysis or vapor depositing. Alternatively, the superconductor can be a thin metal tape disposed on a suitable carrier.

For supporting one or several of such superconductors in the interior of a cryogenic cable constructed from concentrical tube for purposes'of heat protection, it has been suggested to position the conductor strings by means of spacer discs placed at some distance from each other in the cable tube. However, this has the disadvantage that a constant distance and spacing between, for example, respective two of three conductors of a three-phase system in the interior space between respective two adjacent spacer discs cannot be maintained because the conductors are twisted. Insertion of a pipe stud of suitable insulating material and between respective two such spacer discs still did not yield the desired result as considerable difficulties arose for manufacturing such an arrangement.

The difficulties outlined above are overcome in accordance with the invention which suggests to proceed in a different manner. In accordance with the present invention the innermost one of a plurality of concentrically arranged pipe includes a cable system comprised of a plurality of twisted or stranded strings and the superconductor strings form a part of this twisted or stranded string arrangement. The several stranded strings are preferably disposed around a core element. This core element can be separately stranded rope or any other flexible element such as a tube.

Such a cable rope composed of a plurality of strings can actually be manufactured in a manner known per se from stranding conductors and as is known in the art of manufacturing cables in general. Techniques for stranding cables generally have been developed which guarantee that particular strings have constant distance from each other over the entire extension of the stranded rope (cable). Presently now, as particular superconductive strings are included in the stranded rope, they obtain constant distance from each other, and individually they have also a constant distance from the interior wall of the pipe of said concentric pipe system and into which the stranded string assembly (rope) is inserted because the rope has quite uniform diameter or, more precisely, constant overall cross sectional profile. If additional conductor bundles are included, the conductors in the stranded assembly will have constant distance from these additional bundles, particularly if they are likewise constructed as a stranded string assembly.

The uniform positioning of the several superconductive strings included in the stranded arrangements is instrumental in obtaining uniform flow of liquid coolant in relation to and around the superconductor strings so that the conductor surface is constantly in contact with or close to the flowing medium, such as liquid helium, in order to obtain optimum cooling of the several superconductor strings on an overall as well as an incremental basis.

The individual strings constituting the stranded cable rope but other than the superconductors can be made of plastic strings with solid section. However, small plastic tubes can be used instead, and they can be used as additional conduits for the coolant. The superconductors used in this arrangement-of stranded strings may have solid section but they, likewise, can be tubular. The conductors can be provided as superconductive layer placed on a suitable carrier string, such as a plastic or metal string whereby the carrier may have solid section or tubular configuration. For the sake of convenience, the term string shall be used regardless of the section, whether solid or tubular.

The conductor strings may form several layers and the strings of a particular layer may have similar or different diameters in order to match the geometric profile and dimensions of the surrounding pipe forming part of the cryogenic pipe systems as outlined above. The conductors in such a stranded bundle of strings must have a particular distance,

spacing and position in relation to the inner pipe wall of the cryogenic pipe system, and/or particular distance must be maintained in relation to other bundles or ropes likewise contained in that pipe, these additional ropes being, possibly, similarly constructed.

In order to maintain and to control spacing and distance it is advisable to wind an insulating tape or string helically around such a stranded bundle or rope so that the outer dimensions of the bundle or rope as a whole can be controlled. Generally speaking, the stranding techniques suggested here permits rather accurate adaptation of the dimension of the rope to the dimensions of the tube for containing the cryogenic liquid and the conductors.

Generally, it can be assumed that the stranded rope made for positioning one or several superconductive strings requires several layers of string; for this it is advantageous to make such a rope in the following manner. At first, a core bundle or rope is made in layers by using twisting and stranding techniques and using strands or strings of insulating material of the type used conventionally for low-temperature cryogenic engineering. That central or core rope may already include several layers of stranded strings. v I

Next, a layer of superconductive strings is placed and stranded on top of such a core rope whereby, however, the stranding includes the providing of additional insulating strings or thread, respectively interposed between but in the same layer as the superconductive strings. These insulating threads or strings serve as spacer, and they should have the same diameter as the superconductors so that the latter becomes firmly positioned on the core. Moreover, the number and dimension of the insulating spacer strings interposed between respective two of the superconductor strings defines and establishes a definite distance between them.

The bundle thus produced forms a rope upon which another insulating thread is wound to establish another layer for holding the bundle or rope previously produced together. The diameter of that latter string or thread determines the distance of the superconductive strings to the inner wall of the pipe into which the stranded string arrangement thus produced is to be inserted, of, if there are other bundles, this outer thread layer determines the position and relative distance of such a bundle in relation to others of similar or different type.

In lieu of a core bundle made of solid section individual insulating thread or strings one could use tubular ones or one could dispense with employing a core bundle entirely and use a single pipe for serving as core upon which the stranded arrangement of superconductors and insulating thread is being placed. This pipe, as well as the pipes used to establish the cryogenic cable may be corrugated; it can be made of plastic, i.e., it should be made of or be covered by electrical insulation in case a layer containing superconductive strings is directly wound thereon. The superconductive strings can be insulated against the central pipe by a layer of insulating strings wound on the central tube and interposed between the inner pipe and the layer which includes the superconductors. In this case the inner pipe can also be made of metal. This central pipe may serve as principle conduit for the cryogenic coolant and it may have bores extending in longitudinal direction so that the coolant running through this central pipe can also pass into the ring space defined by that pipe and the pipe into which the stranded bundle is inserted and which contains the stranded superconductors.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:

FIG. 1 illustrates a perspective view into the interior of a cryogenic cable constructed in accordance with the preferred embodiment of the present invention.

FIG. 2 is a cross section through the cable shown in FIG. 1; and

FIGS. 3 through 7 illustrate similar cross sections through stranded ropes which include differently constructed superconductive elements and/or insulating strings, constituting additional embodiment of the present invention.

Proceeding now to the detailed description of the drawings, in FIGS. 1 and 2 thereof there is illustrated a pipe I. This pipe is assumed to be the innermost one of a plurality of concentrically arranged pipes serving for thermal insulation and for establishing a controlled temperature gradient to the environment in a manner outlined in the introduction. The pipe 1 is illustrated as a smooth pipe, but it can in fact be a corrugated one.

Pipe 1 has two functions, first it serves as an enclosure for one or several superconductors proper 2, and, secondly, it serves, as conduit for a suitable cryogenic coolant for establishing and maintaining the superconductive state in the superconductors. For example, pipe 1 serves as a passage or conduit for liquid helium. A steady flow of coolant around the superconductors 2 is maintained in pipe 1 through external means. The temperature maintained in the interior of pipe 1 is about 4 Kelvin which is sufficient to maintain suitable superconductors in the superconductive state. For example, superconductors made of niobium alloy are used and form part of the string system which is disposed in and extends along the interior of pipe 1. In FIGS. 1 and 2 there are shown three superconductors 2 which are solid section strings made of such a superconductive material.

It is now important that the superconductor strings 2 pertaining, for example, to a three-phase electrical conductor system have uniform distance from the wall of pipe 1 but more important, it must be assured that the superconductor strings 2 have uniform distance from each other over the entire length of the cable which may be considerable. Such equidistant spacing of the strings is established and maintained as follows.

There is provided a core string 3 made of suitable cryogenic insulation and serving as core for a first layer of strings or thread 4 likewise made of insulating material, preferably of the same material. Strings 4 have been stranded to be twisted in a particular direction or sense of winding. The figure shows a single layer of strings 4, but several layers could be provided. The thus-formed core is provided with another layer which includes a plurality of stranded strings, the twist thereof being reversed relative to the stranded core. This second layer includes additional insulating strings 5 but it also includes the conductor strings 2 whereby in-between respective two strings of superconductive material there are provided, for example, three insulating spacer strings 5. The particular selection of the number of insulating spacer strings depends upon the chosen diameter for the strings and determines the distance between adjacent two of the conductors 2. One can also say there is a single layer of stranded strings provided on a previously made core rope, and a superconductive string is substituted for every fourth string in that layer of the otherwise insulated strings.

As the thus formed bundle of strings including strings 2 and 5 is uniformly twisted around the core, the distance between 2 superconductors is maintained along the entire extension of the rope thus produced. The entire rope thus produced is enveloped by another insulating thread or string 6 helically wound around the arrangement as previously described and again the sense of winding is reversed to the sense of twisting of strings 2 and 5. This way the individual layers are firmly positioned in relation to each other whereby each layer positions particularly the layer underneath in a concentrical relation while, on the other hand, the layer underneath serves as firm support for the layer wound thereon. Therefore, the entire arrangement is held together and the string arrangement as a whole is positively positioned in relation to the inner wall of pipe 1.

The superconductive strings 2 stranded with insulating threads 5 are shown in FIG. 2 as having solid section. As stated, such a string 2 is actually a wire made of a niobium alloy. However, it is possible and frequently of particular advantage to construct the superconductors themselves as little tubes. Such tubes 7 are shown in FIG. 3. These tubes can be included in stranding of the several strings in exactly the same manner. The insulating strings 3, 4 and 5 in FIG. 3 have solid section as in FIG. 2. The overall construction as shown in FIG. 1 is similarly applicable to the arrangement of FIG. 3.

It is sometimes customary to use a superconductive layer which has been electrolytically deposited or vapor deposited upon a carrier. As shown in FIG. 4, for example, the superconductor proper is constituted by a tubular layer of superconductive material 9, disposed on a string like carrier 8 made, for example, of insulating material or any other nonsuperconductive material. Again, the conductor strings thus formed are included in the stranding process to establish a cable system as shown in FIG. 1.

Proceeding now to FIG. 5, there is shown a cable construction wherein plastic or metal tubes 10 serve as carrier upon which respectively superconductive layers 11 are deposited. The thus-formed superconductor strings are also included in a stranded string arrangement forming a rope or bundle as shown in FIG. 1.

In FIG. 6 there is shown an arrangement in which the insulating strings differ. These insulating strings are actually tubes 15 and the interior of the tubes is preferably included as passageway for the liquid coolant. The superconductors are shown again as solid section, superconductive wires, but any of the other superconductor constructions as shown in FIGS. 3, 4 and 5 can be used. For reasons of obtaining sufficient overall stiffness it may be desirable that not all insulating strings are tubes such as 15, so that some insulating strings may have solid sections, others tubular section. This may, for example, differ from layer to layer.

The embodiments previously described have a stranded core. In FIG. 7 there is illustrated a tubular core 13 serving as principal conduit for the coolant, to supply ample cryogenic liquid in free flow to all portions of the possibly, rather long cable. The tube has apertures to permit filling the space between it and tube 1 with coolant. The stranded string layer which includes superconductive wires 2 is wound on top of tube 13. Also, that layer is held together by a string 6, hclically wound on the layer which includes wires 2 but at reversed twist. The superconductive elements could be similar to those in FIGS. 3, 4 and 5, and the insulating spacer strings could be tubes such as shown in FIG. 6.

Independently from the particular shape and cross section of the superconductive strings, it is essential for the invention that they can be included in a stranding operation to form the rope which constitutes now a superconductive cable. As stranding is an operation which can be very accurately controlled, accurately controlled spacing of the superconductive string elements results from the inclusion of insulating strings to obtain definite distance relationships, regardless of profile, over the entire length of the cable. Moreover, particular spatial relationship is maintainable relative to the inner wall of pipe 1. The conditions for cooling each individual superconductor are the same for all of them. This is important as the superconductive state in each of the superconductors is maintained in exactly the same manner to guarantee proper operation of the cable as a whole and to guarantee in particular that the impedance of such a cable is uniform for all of its phases.

The invention is not limited to the embodiments described above but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be included.

Iclaim:

1. Construction for cryogenic cables which includes a pipe as enclosure for superconductive means, comprising a first plurality of individual superconductive strings in the pipe, and

a second plurality of insulating strings stranded with the individual strings of the first plurality so that some of the strings of the second plurality separate the individual strings of the first plurality and are stranded therewith at similar twist to form a ropelike construction disposed in the pipe.

2. Cable construction as in claim 1, including a core, supporting a layer of stranded strings which includes strings of the first and second pluralities.

3. Cable construction as in claim 1, including a stranded string core, and a layer of stranded strings thereon which includes strings of the pluralities.

4. Cable construction as in claim I, at least some strings of the pluralities having solid section.

5. Cable construction as in claim 1, at least some strings of the pluralities having tubular section.

6. Cable construction as in claim 1, at least some strings of the first plurality including a tubular carrier of nonsuperconductive material with a layer of superconductive material.

7. Cable construction as in claim 1, the rope including a core, the core being comprised of a tube, there being at least one layer of stranded strings on the core, the strings pertaining to the first and second pluralities.

8. Cable construction as in claim 7, the tube having apertures to permit passage of cryogenic liquid.

9. Cable construction as in claim 1, the strings of the first plurality pertaining to a layer of strings which includes spacer strings of the second plurality, the strings of the layer having similar twist.

10. Cable construction as in claim 9, the spacer strings having diameter similar to the diameter of the strings of the first plurality.

11. Cable construction as in claim 9, there being insulated string wound hclically upon the layer.

12. Cable construction as in claim 1, the strings of the pluralities stranded in several layers, one layer thereof including the strings of the first plurality with spacer strings of the second plurality interposed in the same layer.

13. Cable construction as in claim 12, the strings of adjacent layers stranded with opposite twist.

14. Cable construction as I claim 1, at least some strings of the first plurality including a tubular solid carrier of nonsuperconductive material with a layer of superconductive material. 

1. Construction for cryogenic cables which includes a pipe as enclosure for superconductive means, comprising a first plurality of individual superconductive strings in the pipe, and a second plurality of insulating strings stranded with the individual strings of the first plurAlity so that some of the strings of the second plurality separate the individual strings of the first plurality and are stranded therewith at similar twist to form a ropelike construction disposed in the pipe.
 2. Cable construction as in claim 1, including a core, supporting a layer of stranded strings which includes strings of the first and second pluralities.
 3. Cable construction as in claim 1, including a stranded string core, and a layer of stranded strings thereon which includes strings of the pluralities.
 4. Cable construction as in claim 1, at least some strings of the pluralities having solid section.
 5. Cable construction as in claim 1, at least some strings of the pluralities having tubular section.
 6. Cable construction as in claim 1, at least some strings of the first plurality including a tubular carrier of nonsuperconductive material with a layer of superconductive material.
 7. Cable construction as in claim 1, the rope including a core, the core being comprised of a tube, there being at least one layer of stranded strings on the core, the strings pertaining to the first and second pluralities.
 8. Cable construction as in claim 7, the tube having apertures to permit passage of cryogenic liquid.
 9. Cable construction as in claim 1, the strings of the first plurality pertaining to a layer of strings which includes spacer strings of the second plurality, the strings of the layer having similar twist.
 10. Cable construction as in claim 9, the spacer strings having diameter similar to the diameter of the strings of the first plurality.
 11. Cable construction as in claim 9, there being insulated string wound helically upon the layer.
 12. Cable construction as in claim 1, the strings of the pluralities stranded in several layers, one layer thereof including the strings of the first plurality with spacer strings of the second plurality interposed in the same layer.
 13. Cable construction as in claim 12, the strings of adjacent layers stranded with opposite twist.
 14. Cable construction as in claim 1, at least some strings of the first plurality including a tubular solid carrier of nonsuperconductive material with a layer of superconductive material. 